dc

Desk calculator.

Syntax
dc

Printing Commands

p Print the value on the top of the stack, without altering the
stack. A newline is printed after the value.
n Print the value on the top of the stack, popping it off, and
do not print a newline after.
P Pop off the value on top of the stack. If it a string, it
is simply printed without a trailing newline. Otherwise it is a
number, and the integer portion of its absolute value is printed
out as a "base (UCHAR_MAX+1)" byte stream.
f Print the entire contents of the stack without altering anything.
This is a good command to use if you are lost or want to
figure out what the effect of some command has been.

dc works with postfix notation; rather like many HP Calculators.
Basic arithmetic uses the standard + - / * symbols
but entered after the digits

so entering:
100 0.5 * p
will return 50

Arithmetic

+ Pop two values off the stack, add them, and push the result.
The precision of the result is determined only by the values of
the arguments, and is enough to be exact.
- Pop two values, subtract the first one popped from the second
one popped, and push the result.
* Pop two values, multiply them, and push the result. The
number of fraction digits in the result depends on the current
precision value and the number of fraction digits in the two
arguments.
/ Pop two values, divide the second one popped from the first
one popped, and push the result. The number of fraction digits
is specified by the precision value.
% Pop two values, compute the remainder of the division that the /
command would do, and push that. The value computed is the
same as that computed by the sequence Sd dld/ Ld*- .
~ Pop two values, divide the second one popped from the first
one popped. The quotient is pushed first, and the remainder is
pushed next. The number of fraction digits used in the division
is specified by the precision value. (The sequence SdSn lnld/
LnLd% could also accomplish this function, with slightly differ-
ent error checking.)
^ Pop two values and exponentiate, using the first value popped
as the exponent and the second popped as the base. The fraction
part of the exponent is ignored. The precision value specifies
the number of fraction digits in the result.
| Pop three values and compute a modular exponentiation. The
first value popped is used as the reduction modulus; this value
must be a non-zero number, and should be an integer. The second
popped is used as the exponent; this value must be a non-nega-
tive number, and any fractional part of this exponent will be
ignored. The third value popped is the base which gets exponen-
tiated, which should be an integer. For small integers this is
like the sequence Sm^Lm%, but, unlike ^, this command will work
with arbritrarily large exponents.
v Pop one value, computes its square root, and pushes that. The
precision value specifies the number of fraction digits in the
result.

Most arithmetic operations are affected by the `precision value',
which you can set with the k command. The default precision value is
zero, which means that all arithmetic except for addition and subtraction produces integer results.

Stack Control

c Clear the stack, rendering it empty.
d Duplicate the value on the top of the stack, pushing another
copy of it. Thus, `4d*p' computes 4 squared and prints it.
r Reverse the order of (swaps) the top two values on the stack.

Registers

Dc provides at least 256 memory registers, each named by a single character. You can store a number or a string in a register and retrieve
it later.

sr Pop the value off the top of the stack and store it into register r.
lr Copy the value in register r and push it onto the stack.
This does not alter the contents of r.
Each register also contains its own stack. The current register value
is the top of the register's stack.
Sr Pop the value off the top of the (main) stack and push it onto
the stack of register r. The previous value of the register
becomes inaccessible.
Lr Pop the value off the top of register r's stack and push it onto
the main stack. The previous value in register r's stack, if
any, is now accessible via the lr command.

Parameters

Dc has three parameters that control its operation: the precision, the
input radix, and the output radix. The precision specifies the number
of fraction digits to keep in the result of most arithmetic operations.
The input radix controls the interpretation of numbers typed in; all
numbers typed in use this radix. The output radix is used for printing
numbers.

The input and output radices are separate parameters; you can make them
unequal, which can be useful or confusing. The input radix must be
between 2 and 16 inclusive. The output radix must be at least 2. The
precision must be zero or greater. The precision is always measured in
decimal digits, regardless of the current input or output radix.

i Pops the value off the top of the stack and uses it to set the
input radix.
o Pops the value off the top of the stack and uses it to set the
output radix.
k Pops the value off the top of the stack and uses it to set the
precision.
I Pushes the current input radix on the stack.
O Pushes the current output radix on the stack.
K Pushes the current precision on the stack.

Strings

Dc can operate on strings as well as on numbers. The only things you
can do with strings are print them and execute them as macros (which
means that the contents of the string are processed as dc commands).
All registers and the stack can hold strings, and dc always knows
whether any given object is a string or a number. Some commands such
as arithmetic operations demand numbers as arguments and print errors
if given strings. Other commands can accept either a number or a
string; for example, the p command can accept either and prints the
object according to its type.

[characters]
Makes a string containing characters (contained between balanced
[ and ] characters), and pushes it on the stack. For example,
[foo]P prints the characters foo (with no newline).
a The top-of-stack is popped. If it was a number, then the low-
order byte of this number is converted into a string and pushed
onto the stack. Otherwise the top-of-stack was a string, and
the first character of that string is pushed back.
x Pops a value off the stack and executes it as a macro. Normally
it should be a string; if it is a number, it is simply pushed
back onto the stack. For example, [1p]x executes the macro 1p
which pushes 1 on the stack and prints 1 on a separate line.

Macros are most often stored in registers; [1p]sa stores a macro to
print 1 into register a, and lax invokes this macro.

>r Pops two values off the stack and compares them assuming they
are numbers, executing the contents of register r as a macro if
the original top-of-stack is greater. Thus, 1 2>a will invoke
register a's contents and 2 1>a will not.
!>r Similar but invokes the macro if the original top-of-stack is
not greater than (less than or equal to) what was the second-to-
top.
<r similar but invokes the macro if original top-of-stack is less.
!<r similar but invokes the macro if original top-of-stack is not less
than (greater or equal to) what was second-to-top.
=r similar but invokes the macro if two numbers popped are equal.
!=r similar but invokes the macro if two numbers popped are not equal.
? Reads a line from terminal and executes it. this command
allows to request input user.
q exit from a macro and also from the macro which invoked it. If called from the
top level, or from a macro which was called directly from the top level, the q
command will cause dc to exit.
Q Pop a value off the stack and uses it as a count of levels of macro execution
to be exited. Thus, 3Q exits three levels.
The Q command will never cause dc to exit.

Status Inquiry

Z Pop a value off the stack, calculates the number of digits it has (or number of
characters, if it is a string) and pushes that number.
X Pop a value off the stack, calculates the number of fraction digits it has, and
pushes that number. For a string, the value pushed is 0.
z Push the current stack depth: the number of objects on the stack before the
execution of the z command.

Miscellaneous

! Will run the rest of the line as a system command. Note that parsing of the !<,
!=, and !> commands take precedence, so if you want to run a command starting
with <, =, or > you will need to add a space after the !.
# Will interpret the rest of the line as a comment.
:r Will pop the top two values off of the stack. The old second-
to-top value will be stored in the array r, indexed by the old
top-of-stack value.
;r Pop the top-of-stack and uses it as an index into the array r.
The selected value is then pushed onto the stack.

Note that each stacked instance of a register has its own array associated with it. Thus 1 0:a 0Sa 2 0:a La 0;ap will print 1, because the 2
was stored in an instance of 0:a that was later popped.

“The best way to destroy the capitalist system is to debauch the currency” ~ John Keynes